Nova Velorum 1993
in the constellation Vela
8 to 9 times the mass of the Sun
Diameter roughly equal to a large city
GRS 1009-45 was discovered in September 1993, when it produced a sudden outburst of gamma rays and X-rays that was detected by a Soviet space telescope. Astronomers categorized the outburst as an X-ray nova.
Such a nova occurs in a system in which a black hole or neutron star is stealing hot gas from the surface of a nearby companion star. The gas spirals toward the compact object, forming a superhot accretion disk.
If the disk becomes unstable, its material crashes toward the black hole. As the gas piles up it gets hotter and hotter, triggering an explosion that produces a torrent of gamma rays and X-rays.
By watching the intensity of the outburst at different wavelengths, measuring how quickly it faded, and looking for follow-up outbursts, astronomers determined that the outburst almost certainly came from a black hole and not a less-dense neutron star.
Observations with telescopes at Las Campanas Observatory in Chile revealed from 2007 to 2010 showed that the companion star is spinning at about 200,000 miles (310,000 km) per hour. Combined with information on the orbit of the two objects (they orbit each other once every 6.9 hours at a distance of about 1.5 million miles (2.5 million km)), astronomers measured the masses of both bodies. The black hole is about 8.5 times the mass of the Sun, with the companion star, a red dwarf, no more than one-half the Sun's mass.
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This document was last modified: February 12, 2012.